This invention relates to drilling tools and more particularly to a straight pull variable impact jarring mechanism for releasing objects stuck in a well bore.
Well jars are known for imparting sharp jarring forces to an object stuck in a well bore. One prior art well jar has tubular shaped inner and outer telescoping elements. Inclined surfaces are affixed on the inner mandrel, and a roller, for each inclined surface, is mounted on the outer telescoping element. Each roller and corresponding inclined surface form a latch. An elongated open space extends in the inner element along the ends of the inclined surfaces into which the rollers move upon release of the latches. Coacting impact faces, one on each of the telescoping elements, impact at one extremity of longitudinal movement of the telescoping elements. One of the telescoping elements is for connection to the lower end of an upper drill string and the other telescoping element is for connection, for example, to an object stuck in a well bore. The latches hold the telescoping elements against relative longitudinal movement. In one mode of operation the latches are released by rotating the telescoping elements until the rollers and inclined surfaces of the latches are disengaged at which time the rollers enter the opening and the telescoping elements are allowed to freely move longitudinally relative to each other under an applied longitudinal force, causing the coacting impact faces to impact. Alternately, a torsion can be applied through the drill string to the corresponding telescoping element causing the inclined surfaces and rollers to be urged toward the latched position. A downward longitudinal force on the drill string of sufficient magnitude will cause an interaction of the rollers and inclined surfaces which rotates the telescoping elements against the applied torsion until the rollers reach the elongated opening, allowing the longitudinal force to drive the coacting impact surfaces into impact. Such an arrangement relies on torsion applied to the drill string to determine the magnitude of the longitudinal force required for a release of the latches. Additionally, the magnitude of the impact of the coacting faces depends on the magnitude of the torsion in the drill string. With such an arrangement, it is difficult to determine precisely the torsional forces on the jar, particularly when it is at the lower or end of a very long drill string. Additionally, momentary longitudinal forces on the jar, such as those caused by sudden braking of the drill string, may cause the jar to inadvertently release during a drilling operation. Additionally when rotating the drill string the inner and outer telescoping elements rotate relative to one another in one direction until the rollers engage the inclined surfaces and in the opposite direction until stops engage.
An alternate prior art well jar also utilizes tubular shaped inner and outer telescoping elements with coacting impact faces. However, this device is provided with a tubular shaped intermediate sleeve member which carries inclined surfaces defining lateral notches. A longitudinally extending opening extends into the intermediate member along the ends of the notches. The inner telescoping element carries lugs which combine with the inclined surfaces to form latches. A spline connection is provided between the inner and outer telescoping elements to transmit torque directly from one to the other during a drilling operation. A torque spring is connected between the outer telescoping element and the intermediate member which rotates the intermediate member in a direction which engages the lugs in the notches. A longitudinal force applied in one direction between the telescoping elements will cause the adjacent surfaces of the notches and lugs to slide relative to each other, causing the intermediate member to be forced to rotate against the urging of the torsion spring. When the force on the intermediate member is of sufficient magnitude to overcome the torsion spring, the rotation is sufficient that the lugs enter the longitudinal opening at which point the telescoping elements freely move longitudinally relative to each other to one extremity where the coacting impact faces strike. With the splined connection between the inner and outer telescoping elements, a direct torque drive is provided between the telescoping elements during a drilling operation. However, momentary longitudinal forces applied between the telescoping elements of sufficient magnitude to overcome the torsion spring will cause the latches to release even though the user does not want the jar to release at that moment.
A further alternate prior art well jar also has inner and outer tubular telescoping elements. An elongated opening and lateral V-shaped notches opening into the opening are provided in the inner telescoping element. Latches are formed by a V-shaped wedge for each notch, on the outer telescoping element. The notches and wedges of each latch have adjacent inclined surfaces which slide against the adjacent surface to cause a relative rotation of the telescoping elements. With the V-shaped notches and wedges, either tension or compression longitudinally between the telescoping elements will force the inner and outer telescoping elements to rotate relative to each other until the wedges enter the elongated opening and release, allowing the telescoping elements to move longitudinally until the coacting impact faces come together. A coupling on the inner telescoping element has a spline connection to the outer telescoping element for transmitting torque directly between the outer telescoping element and the coupling. The inner telescoping element is rotatable relative to the coupling, as well as the outer telescoping element, and a torsion spring is connected between the inner telescoping element and the coupling for urging the notch and wedges into engagement. Couplings for connection to an upper drill string and to a stuck object are provided on the coupling and outer telescoping element. Similar problems exist with respect to this device as mentioned with respect to the prior mentioned device.